Adaptive predistortion for a transmit system

ABSTRACT

Systems, methods, and devices relating to the provision of deliberate predistortion to an input signal to compensate for distortions introduced by an amplifier subsystem. An input signal is received by a predistortion subsystem which applies deliberate predistortions to the input signal to arrive at a predistorted signal. The predistorted signal is received by an amplifier subsystem which decomposes the signal, processes the decomposed signal, and then recombines the components to arrive at a system output signal. The predistortion subsystem adaptively adjusts the predistortions based on characteristics of the system output signal. A feedback signal, a replica of the system output signal, is used in updating lookup table entries used to determine the predistortion.

FIELD OF THE INVENTION

The present invention relates generally to power amplification systemsand is specifically applicable but not limited to power amplificationsystems using a Chireix architecture.

BACKGROUND TO THE INVENTION

The recent revolution in communications has caused a renewed focus onwireless technology based products. Mobile telephones, handheldcomputers, and other devices now seamlessly communicate using wirelesstechnology. One component that forms the core of such technology is theamplifier. Wireless devices require high efficiency amplifiers to notonly extend the range of their coverage but also to conserve the limitedbattery power that such devices carry.

One possible architecture which may be used for such a power amplifieris called a Chireix architecture. Named after Henry Chireix who firstproposed such an architecture in the 1930s, the Chireix architecture hasfallen out of favor due to its seemingly inherent limitations. However,it has recently been revisited as it provides some advantages that otherarchitectures do not have.

While the Chireix architecture provides some advantages, the processwhich the input signal undergoes also introduces some drawbacks.Specifically, distortions are introduced into the signal by thecomponents in the Chireix based amplifier/modulator system. Thesedistortions may also change over time and may therefore lead to atime-varying “drift” or change in the signal. Such distortions,time-varying or not, have led to problems that are not only inconvenientbut expensive as well.

Based on the above, there is therefore a need for an amplifier systemwhich provides the benefits of a Chireix based amplifier but which alsocompensates for or avoids the distortions which a Chireix basedamplifier introduces. Such an amplifier system should adjust todiffering conditions, preferably with little or no user intervention. Itis therefore an object of the present invention to provide alternativeswhich mitigate if not overcome the disadvantages of the prior art.

SUMMARY OF THE INVENTION

The present invention provides systems, methods, and devices relating tothe provision of deliberate predistortion to an input signal tocompensate for distortions introduced by an amplifier subsystem. Aninput signal is received by a predistortion subsystem which appliesdeliberate predistortions to the input signal to arrive at apredistorted signal. The predistorted signal is received by an amplifiersubsystem which decomposes the signal, processes the decomposed signal,and then recombines the components to arrive at a system output signal.The predistortion subsystem adaptively adjusts the predistortions basedon characteristics of the system output signal. A feedback signal, areplica of the system output signal, is used in updating lookup tableentries used to determine the predistortion.

In a first aspect, the present invention provides a system forprocessing an input signal, the system comprising:

-   -   an adaptive predistortion subsystem for receiving said input        signal and for producing a predistorted signal by applying a        deliberate predistortion to said input signal; and    -   a signal processing subsystem receiving and processing said        predistorted signal and producing a system output signal,        wherein    -   said predistortion subsystem distorts said input signal to        compensate for distortions in said system output signal;    -   said signal processing subsystem decomposes said predistorted        signal into separate components, each of said separate        components being processed separately;    -   said processing subsystem combines said components after        processing to produce said system output signal; and    -   said deliberate predistortion applied to said input signal by        said adaptive predistortion subsystem to produce said        predistorted signal is adjusted based on characteristics of said        system output signal and said input signal.

In a second aspect the present invention provides a method of processingan input signal to produce a system output signal, the methodcomprising:

-   -   a) receiving said input signal;    -   b) applying a deliberate predistortion to said input signal to        result in a predistorted signal;    -   c) decomposing said predistorted signal into at least two        component signals;    -   d) combining said at least two component signals to produce said        system output signal;    -   e) adjusting said deliberate predistortion based on said        characteristics of said system output signal.

In a third aspect the present invention provides an adaptivepredistortion subsystem for use with a signal processing system whichproduces a system output signal, the predistortion subsystem comprising:

-   -   determining means for determining a deliberate predistortion to        be applied to an input signal;    -   adjustment means for applying said deliberate predistortion to        said input signal;    -   update means for periodically updating said determining means        based on characteristics of said system output signal.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the invention will be obtained by consideringthe detailed description below, with reference to the following drawingsin which:

FIG. 1 is a block diagram of a Chireix architecture amplifier subsystem;

FIG. 2 is a block diagram of an amplifier system using the subsystem ofFIG. 1 and a predistortion subsystem;

FIG. 3 is a detailed block diagram of the internal components of thepredistortion subsystem;

FIG. 4 illustrates the amplifier system of FIG. 2 and incorporating afeedback signal used by the predistortion subsystem of FIG. 3;

FIG. 5 is a block diagram of a delay line circuit which maybe used inthe system of FIG. 4;

FIG. 6 is a detailed block diagram of one embodiment of a Chireixamplifier subsystem;

FIG. 7 is a block diagram of a signal processing system according toanother embodiment of the invention; and

FIG. 8 is a detailed block diagram of a system incorporating the featureshown in FIGS. 3, 4 and 7.

DETAILED DESCRIPTION

For clarity, the following terms are to be used with the followingdefinitions:

-   -   AM (amplitude modulation) refers to the AM of an RF (radio        frequency) signal and is equal to the magnitude of the RF        signal's complex base band equivalent    -   PM (phase modulation) refers to the PM of an RF signal and is        equal to the phase of the RF signal's complex base band        equivalent.

Referring to FIG. 1, a block diagram of a Chireix architecture amplifiersubsystem 10 is illustrated. A signal decomposer 20 receives an inputcomplex baseband signal 30. Phase modulated signals 80A, 80B areproduced after the decomposed output of the decomposer 20 are phasemodulated by phase modulation circuitry 85A, 85B. These phase modulatedsignals 80A, 80B are received by power amplifiers 90A, 90B. The phasemodulated signals are thus amplified by the power amplifiers 90A, 90Band are received by a signal combiner 100. The system output signal 110(an RF signal corresponding to the input baseband signal 30) is outputfrom the combiner 100 and is an amplified and modulated version of theinput signal 30. Phase modulation of the phase modulated signals 80A,80B is executed by the signal decomposer 20. The input signal 30 isseparated into at least two components and these at least twocomponents, after phase modulation, are the signals 80A, 80B.

As noted above, the Chireix architecture amplifier subsystem 10 has beenknown to introduce distortions in the system output signal 110. Tocompensate for such distortions, a predistortion subsystem 120 isprovided. Referring to FIG. 2, the predistortion subsystem 120 receivesthe input signal 30 and produces a predistorted signal 130. Thepredistorted signal 130 is received by the amplifier subsystem 10. Theamplifier subsystem then produces the system output signal 110.

The distortions for which the predistortion subsystem is to compensatemay come as a phase distortion, a magnitude distortion, or as acombination of both. It has been found that, without predistortion, thesystem output signal 110 has an amplitude modulation (AM) that is notequal to the expected and desired AM. Furthermore, the phase modulation(PM) of the system output signal 110, if predistortion is not present,deviates from the expected and desired PM. Experiments have found thatthe AM distortion or error (magnitude distortion) depends on the AM ofthe input signal. Also, it has been found that the PM distortion (orphase distortion) depends on the AM of the input signal.

As noted above, one solution to the above issues is to predistort theinput signal as detailed in FIG. 2. Further details on this approach canbe found in co-pending application entitled Predistortion Circuit For aChireix Power Amplifier Transmit System and filed with the US Patent andTrademark Office, the whole of which is incorporated herein byreference. While the predistortion solution does work, it is not asrobust and as fault tolerant as may be desirable. An adaptivepredistortion subsystem 200, as illustrated in FIG. 3, would compensatefor conditions and for other distortions which the system output signalmay have.

Referring to FIG. 3, a block diagram of such an adaptive predistortionsubsystem is illustrated. The adaptive predistortion subsystem 200 ofFIG. 3 may be used in place of the predistortion subsystem 120 of FIG.2.

While an analog implementation of the subsystem 200 is possible, it hasbeen found that a digital implementation was simpler to achieve. Assuch, the following description assumes that the input signal 30 is adigital signal having a digital representation of the desired AM and itsPM of the output RF signal. Digital AM/AM predistortion modifies themagnitude of the complex digital input signal such that the RF outputsignal has the desired AM, despite the distortion. Digital AM/PMpredistortion modifies the phase of the complex digital input signalsuch that the RF output has the desired PM, despite the distortion.

As can be seen in FIG. 3, multiple components are involved in theadaptive prdistortion subsystem 200: a Cartesian to polar conversionunit 210, a magnitude value lookup table (LUT) block 220, a magnitudeupdate block 230, a magnitude delay block 240, a phase value lookuptable (LUT) block 250, a phase value update block 260, a phase delayblock 270, and an adder 280. The digital input signal 30 is converted bythe conversion unit 210 from Cartesian coordinates to polar coordinates.The magnitude of the converted signal is then received and used by thelookup table blocks 220, 250 to determine the proper amount ofpredistortion to be applied. The phase lookup table 250 adds the phasedistortion to the converted signal by way of the adder 280. Thepredistorted signal is then passed on to the amplifier subsystem 10.

It should be noted that the predistortion modification, defined as anydeliberate distortion which has been introduced to the input signal tochange at least the phase or magnitude of the input signal, can takemany forms. FIG. 3, provided merely for illustrative purposes, depictstwo types of predistortion—phase predistortion and magnitudepredistortion. These two types, separately or together, can make up thepredistortion modification. In some applications, only a magnitude typepredistortion modification may be required while in others only a phasetype predistortion modification is required. In the embodiment explainedhere, the two types of predistortion, together comprise thepredistortion modification.

To account for changing conditions and to acquire appropriate LUTentries, a feedback mechanism is employed to adjust or adapt the lookuptable entries in lookup table blocks 220, 250. Delay blocks 240, 270ensure that the feedback sample is mated with the proper value of theinput signal waveform when processing and updating the lookup tableentries in lookup table blocks 220, 250.

The conversion unit 210, while present, is not necessary but merelyconvenient and makes the predistortion easier to accomplish. As is wellknown, signal representations using Cartesian coordinates take the formof z=x+j y where x and y are the real and imaginary components. Polarcoordinates take the form of z=Ae^(jφ) where the magnitude of the signalis A and its phase is φ. Since both the magnitude and the phase of thesignal is to be modified by the predistortion subsystem, it is clearlymore convenient to accomplish this if the signal were in polarcoordinates. Again as is well known, A=(x²+y²)^(1/2) while φ=tan⁻¹(y/x). Once the signal has been converted into polar coordinates,adjusting the magnitude is as simple as replacing the digitalrepresentation of A by another number. Similarly, the phase can beadjusted by adding a phase correction to the phase of the signal.

After the digital input signal is received and converted by theconversion unit 210, the signal is now represented by two values—amagnitude value 290 and a phase value 300. FIG. 3 shows the differentsignal paths followed by these values—one path for the magnitude value290 and a second path for the phase value 300.

As noted above, the magnitude value 290 can be easily replaced by thepredistorted magnitude value. This is done by way of magnitude lookuptable block 220. The lookup table internal to the magnitude lookup tableblock 220 represents an input/output relationship with the input beingthe undistorted magnitude and the output being the predistorted signalmagnitude. Thus, if the magnitude LUT block 220 has a table entry withan input value of 0.5 and an output value of 0.4, then if theundistorted magnitude value received by the magnitude LUT block 220 is0.5, then this value is replaced with 0.4 as the output of the magnitudeLUT block 220. Based on the LUT (lookup table) entries, the magnitude ofthe unidistorted signal is therefore replaced with the desiredpredistorted magnitude.

Similar to the above, the phase value of the converted input signal isadjusted as well. As can be seen in FIG. 3, the magnitude value 290 isalso received by the phase lookup table block 250. The phase lookuptable block 250, based on the magnitude value, determines the properamount of phase adjustment and adds this phase adjustment to the phasevalue 300 by way of the adder 280. The phase lookup table block 250 alsohas a lookup table resident within the phase LUT block 250 that detailsthe appropriate phase adjustments for given magnitude values.

While the above described magnitude LUT replaces a desired value for thereceived magnitude, other implementations are possible. Instead of adirect replacement value, the magnitude LUT may provide a correctivevalue to the received magnitude. This corrective value can, depending onthe implementation, be an additive or a multiplicative corrective value.

The adaptive predistortion subsystem 200 in FIG. 3 is adaptive in thatthe values of the lookup table entries in the lookup table (LUT) blocks220, 250 change over time to account for changing conditions or foracquiring appropriate LUT entries. This adaptability is implemented byway of a feedback signal tapped from the system output signal 110.Referring to FIGS. 3 and 4, two feedback signals, a magnitude feedbacksignal 310 and a phase feedback signal 320, are received by themagnitude value update block 230 and by the phase value update block 260respectively. These two feedback signals result from processing of thesystem output signal 110 by the analog/digital (A/D) converter 330, theCartesian to polar conversion unit 340, demodulation module 335, andfiltering module 337. As can be seen in FIG. 4, the system output signal(an analog signal) is tapped and this tapped signal 345 is received bythe A/D converter 330 for conversion from an analog to a digital signal.

After conversion to a digital signal, the feedback signal is convertedfrom Cartesian to polar coordinates by the conversion unit 340. Thetapped signal 345 is thus represented by the two feedback signals—themagnitude feedback signal 310 and the phase feedback signal 320. Asmentioned above, both these feedback signals are received by theirrespective update blocks 230, 260.

Once the two digital feedback signals are received, they are thencompared with the delayed input signal coming from the delay blocks 240,270. The updated values for the LUT entries are then calculated andentered into their respective lookup tables. It should be noted that thecomparison may be done by subtracting the feedback signals from thedelayed input signal.

To further elaborate on the above process, the update process isdependent on the difference between the tapped system output signal 345and the input signal 30. This difference is, of course, taken after bothsignals are in polar coordinates. The magnitude and phase errors aredefined as:e _(m)(k)=|z(k)|−|x(k)|e _(φ)(k)=(∠z(k)−∠x(k))wheree_(m)(k)=magnitude errore_(φ)(k)=phase errorz(k)=magnitude of feedback signal (signal 310)x(k)=magnitude of input signal (signal 290)∠z(k)=phase angle of feedback signal (signal 320)∠x(k)=phase angle of input signal (signal 300)

For the magnitude LUT entries in the magnitude LUT block 220, twovariables are defined and used in the process:δ_(F)=−μ_(F) ·e _(m)(k)whereδ_(F)=update quantity dependent on the differences between themagnitudes of the input signal and of the feedback signalμ_(F)=an update speed parameter μ (user selectable), typically μ_(F)>0.

Since the magnitude LUT has LUT entries, each entry is given an entryaddress of n with 0≦n≦N−1, N being the maximum number of entries in theinternal magnitude LUT in the magnitude LUT block 220.

An interpolation distance s is defined as s=αM−n where n=└αM┘ (or thelargest integer value less than or equal to αM), M=|x(k)|, and α is ascaling value applied such that the magnitude range (e.g. 0≦M<1) ismapped to a table index range 0≦n≦(N−1).

The table entries are thus updated using the following formulae (n beingone table address and n+1 being another table address):F _(n)(k+1)=F _(n)(k)+(1−s)·δ_(F) iff0≦n≦(N−1)F _(n+1)(k+1)=F _(n+1)(k)+(s)·δ_(F) iff0≦n+1≦(N−1)whereF_(n)(k)=table entry n for time sample kF_(n)(k+1)=table entry n for time sample k+1F_(n+1)(k)=table entry for n+1 for time sample kF_(n+1)(k+1)=table entry n+1 for time sample k+1

From the above equations, it should be clear that one, two or no entriesin the internal magnitude LUT are updated depending on the value of αM.Thus, for this implementation, depending on the value of αM, one ofF_(n) and F_(n+1) is updated, both are updated, or neither is updated.Other implementations, depending on the circumstances and needs of theparticular application, may update other numbers of entries.

For the phase LUT entires, an analogous process is used in the phaseupdate block 260. An update quantity is defined:δ_(G)=−μ_(G) ·e _(φ)(k)whereδ_(G)=update quantity dependent on the differences between the phaseangles of the input signal and of the system output signalμ_(G)=an update speed parameter (user selectable) where 0≦μ_(G)<1

Using the parameter s as defined above for the magnitude LUT, the phaseLUT be updated using the following formulas:G _(n)(k+1)=G _(n)(k)+(1−s)·δ_(G) iff 1≦n≦(N−1)G _(n+1)(k+1)=G _(n+1)(k+1)+(s)·δ_(G) iff 1≦n≦N

Again, much like the magnitude LUT entry update process, the updateprocess for the phase entries will, depending on the value of αM, updateone, two, or none of the phase LUT entries.

It should be noted that LUT adaptation may involve updating more thantwo entries with some weighting applied. As an example, the weightingmay depend upon the distance of the LUT entry from the update point. Thediscussion herein is based upon the use of two entries and the use of aninterpretation distance.

As an example of the above processes, a phase entry update will beillustrated. For this example, the following values are assumed:N=6M≦1α=5x(k)=0.35exp(j·2·7)z(k)=0.2exp(j·3·1)μ_(G)=0.1

Thus, M=0.35 and αM=1.75. Thus, n=1 (since the lowest integer value lessthan or equal to 1.75=1) and n+1=2. From these values, s=1.75−1=0.75.Given that z(k)=0.2 exp(j·2.3), the e_(φ)(k)=−0.4. Thus,δ_(G)=−(0.1)(−0.4)=+0.04. The required correction for G₁ is therefore

(1−s)·δ_(G)=(1−0.75)(+0.04)=0.25·(+0.04)=0.01. For G₂, the correction iss·δ_(G)=(0.75)(0.04)=0.03. The new values are therefore:G ₁(k+1)=G ₁(k)+0.01G ₂(k+1)=G ₂(k)+0.03

This update is illustrated by the values in the following table: LUTcontent LUT content Address (n) before update Correction after update 0−1 0 −1 1 2 0.01 2.01 2 −0.5 0.03 −0.47 3 −0.5 0 −0.5 4 0.5 0 0.5 5 2 02

It should be noted that the above process also takes into account thelookup of values that are not to be found in the internal lookup tables.Linear interpolation using s=αM−n is used for magnitude values thatcannot be found in the lookup table entries. As an example, if themagnitude is given as 0.35 but the only table entries are 0.3 and 0.4,linear interpolation is used. The following formula is used to findvalues not found in the lookup tables:F(M)=(1−s)·F _(n) +s−F _(n+1)whereF_(n)=table value AF_(n+1)=table value B with the desired value being between table valuesA and Bn=└αM┘ (the largest integer value less than or equal to αM)s=αM−nα=scaling value as defined above.

From the above discussion, it should be fairly clear that two of thevalues underpinning most of the calculations are the values for e_(m)(k)and e_(φ)(k), the magnitude and phase errors. For proper synchronizationbetween the relevant input signal and the relevant feedback signal (i.e.the tapped system output signal 345), the input signal must be properlydelayed so that samples from the interpolated input waveform, asobtained from the delayed input signal samples, are mated with therelevant system output signal sample. Such proper delaying shouldtherefore take into account most, if not all, the time delay involved inthe processing production, and feedback of the system output signal(round trip delay). This round trip delay is denoted as τ (seconds) and,before the LUT updating begins, the delay blocks 240, 270 acquires thedelay and delays the input signal accordingly so as to time-align theinput signal samples with the incoming feedback signal.

To implement this delay, a delay line is used with a depth of K, meaningK samples of the input signals may be stored in the delay line. Asshould be clear, each of the K samples were sampled at differentinstances in time. The value of K is predetermined and should be enoughto allow for the maximum possible path delay between the input signaland the feedback signal. These delays are due to a combination of any ofthe following: digital pipelining, analog and digital filter groupdelays, analog propagation delays, and the system and implementationdependent delays.

Because of this delay, a time delayed version of the input signal,x_(δ)(k) is defined and this is ideallyx _(δ)(k)=x(k−δ)whereδ=τ·F _(s)F_(s)=signal sampling rateτ=delay (normal trip delay between input and system output signalfeedback)

To obtain a better result for x₆₇(k), linear interpolation is used toallow for fractional values of δ. Thus, the delay is divided into twoparts κ, the integer part of the sample (representing a discrete sampledelay at the sample rate F_(s)), and ν, a fractional sample of thedelay.

Using this notation, the delayed portion of the input signal can berepresented as:x _(δ)(k)=(1−ν)·x(k−κ)+ν·x(k−κ+1)whereδ=τ·F _(s)κ=└δ┘ν=δ−κAs can be seen, for an integer δ, x_(δ)(k)=x(k−δ).

The above Cartesian equation can be applied to polar representations byhaving separate delay lines for magnitude (|x_(δ)(k)|) and phase(∠x_(δ)(k)) using the sequences |x(k)| and ∠x(k). These are given by:∠x _(δ)(k)=(1−ν)·∠x(k−κ)+ν·∠x(k−κ+1)|x _(δ)(k)|=(1−ν)·|x(k−κ)|+ν·|x(k−κ+1)|It should be fairly clear that x₆₇ (k) is calculated from the samplesx(k), x(k−1), x(k−2), . . . x(k−κ), samples of the input signal taken attime k, k−1, k−2, . . . k−κ.

The above equations for ∠x_(δ)(k) has a peculiarity that is due to theway angle values work. Since ∠x(k−κ) and ∠x(k−κ+1) are represented bymodulo 2π radians (360 degrees) and since −π≦∠x(k)≦π, then errors couldeasily occur.

Thus, if −π≦∠x(k)≦π, and if |∠x(k−κ+1)−∠x(k−κ)|≧π, then∠x_(δ)(k)=(1−ν)·∠x(k−κ)+ν·(∠x(k−κ+1)+2π) if ∠x(k−κ+1)≦∠x(k−κ)

The above described delay can be implemented by cascaded delay elementsand associated sample storage. FIG. 5 illustrates such a delay subsystemwhich can be used as delay blocks 240, 270. As can be seen, delayelements 242A, 242B, 242C, 242D, 242E are cascaded and provide delaysand storage for input signal samples 244A, 244B, 244C, 244D, 244E.Switches 245A, 245B, 245C, 245D, 245E allow any one of the signalsamples 244A-244E to be switched so that it can be used. These samples244A-244E can be weighted accordingly by programmable weighting blocks246A, 246B, 246C, 246D, 246E. The weighted samples are then summed up byadder 248 to produce the delayed signal 249 to be used by the system.The switches 245A . . . 245E and the values in the weighting blocks 246A. . . 246E may be user/system controllable so that any combination ofweighted samples may be produced.

As an example, if τ·F_(s)=2.4 samples is required, then a value of 0.6is used by the weighting block 246C and a value of 0.4 is used by theweighting block 245D. Then, by closing switches 245C and 245D then thesample x(k−2.4) is obtained.

The feedback signal (the tapped system output signal 345 which is areplica of the system output signal 110) may be further processed toachieve better results. As an example, the gain and/or phase of thisreplica of the system output signal may be adjusted for bettercoordination with the delayed replica of the input signal.

Regarding the amplifier subsystem 10, FIG. 6 illustrates one embodimentof the subsystem 10. In FIG. 6, the signal decomposer 20 of FIG. 1comprises a phasor fragmentation engine 20A along with phase modulationunits 60A, 60B. The fragmentation engine 20A receives the magnitude (M)and phase (φ) representing the predistorted signal. The phasorfragmentation engine 20A deconstructs a predetermined modulationwaveform (the predistorted signal) into signal components which are ofequal and constant magnitude. Further information regarding the phasorfragmentation engines may be found in the applicant's co-pendingapplication U.S. application Ser. No. 10/205,743 entitled COMPUTATIONALCIRCUITS AND METHODS FOR PROCESSING MODULATED SIGNALS HAVINGNON-CONSTANT ENVELOPES, which is hereby incorporated by reference. InFIG. 6, these signal components are denoted by angles α and β. Thesecomponents are each received by RF modulation and filtering blocks 60A,60B which process the components to produce RF modulated and filteredversions of the components. The signal component 70A is an RF signalwith phase a while signal component 70B is an RF signal with phase β.These components 70A, 70B are then amplified by amplifiers 90A, 90B. Theamplified components are then recombined using combiner 100. It shouldbe noted that the phase modulation, also known as carrier modulation,may also introduce some undesired amplitude modulation. Signaldecomposition methods other than the phasor fragmentation referred toabove may also be used by the signal decomposer 20.

Regarding the Chireix architecture amplifier subsystem 10, it has beenfound that, for higher amplification efficiencies, switch modeamplifiers are preferred for the amplifiers 90A, 90B. Such switch modeamplifiers, specifically Class D and Class F power amplifiers, providelow output impedances that allow higher amplification efficiencies. Aco-pending application filed on Oct. 16, 2002 and having U.S. Ser. No.10/272,725 entitled CHIREIX ARCHITECTURE USING LOW IMPEDANCE AMPLIFIERSprovides further information on the desirable components and is herebyincorporated by reference. Such types of amplifiers are not required forthe invention to function but they have been found to provideperformance at a desirable level.

It should further be noted that while those are only two parallelamplifiers 90A, 90B in FIG. 1 and FIG. 6, multiple parallel amplifiersmay be used as long as the decomposer 20 decomposes the predistortedsignal 130 into enough components so that each component is separatelyamplified and phase modulated in parallel with the other components.

It should also be noted that the predistortion subsystem 10 explainedabove does not linearize a power amplifier as is well-known in thefield. Instead, the predistortion subsystem linearizes a whole poweramplifier system—the output of the whole amplifier system is linearizedand not simply the output of a single amplifier. Also, unlike thelinearizing systems for power amplifiers that are currently known, theamplifier system discussed in this document compensates for distortionsthat mostly occur at mid signal amplitudes. Current single amplifierlinearization systems linearize distortions that occur at large signalamplitudes.

It should further be noted that the invention may be applied to anysignal processing system which decomposes a signal into components andrecombines them. It has been found that signal combiners (block 100 inFIG. 1) invariably cause distortions. These combiners use addition torecombine the components and improper signal addition, such as whenrecombining sinusoidal components, has been found to be one cause of thedistortions in the system output signal. In the above embodiment, thephasor fragmentation engine decomposes the incoming signal into vectorsand the improper addition of these vectors by the combiner 100 lead todistortions in the output signal.

While the above embodiment amplifies the input signal, albeit separatelyfor each component, this need not be the only signal processingaccomplished after the input signal is decomposed. Referring to FIG. 7,such a generalized system (which could be part of a larger signaltransmission system) is illustrated. The predistortion subsystem 120predistorts an incoming signal 30 and compensates for distortionsintroduced in the system output signal 110 by the improper or imperfectrecombining of the input signals components. These components areproduced by the signal decomposer 20 and are separately processed bysignal component processor blocks 75A, 75B. The processing executed bythe blocks 75A, 75B may take the form of amplification (as in theembodiment above), phase modulation, a combination of the two, or anyother signal processing which may be desired. As an example, each of thesignal components illustrated in FIG. 6 may be separately phasemodulated in addition to being amplified by amplifiers 90A-90B. Thephase modulation may be accomplished separately or be incorporated inthe signal decomposer or, as contemplated for the implementationillustrated in FIG. 6, incorporated into the modulation and filteringblocks 60A, 60B.

As can be seen in FIG. 7, the signal processing subsystem 10A receivesthe predistorted signal from the predistortion subsystem 120. Afterbeing received, the predistorted signal is decomposed by the signaldecomposer 20 into components. These components are then separatelyprocessed by the signal component processor blocks 75A, 75B and are thenrecombined by the recombiner 100.

A feedback signal processing block 400 receives a portion of the systemoutput signal 110 and processes this portion so it may be used by theadaptive predistortion subsystem 120. As an example, the feedback signalprocessing block 400 may contain the A/D converter 330, the conversionunit 340, the filtering module 337, and the demodulation module 335illustrated in FIG. 4. The same block 400 may also contain processingblocks 410, 420 for adjusting the magnitude and/or phase of the feedbacksignal.

One advantage using the above invention is that it allows less stringenttolerances to be used for the system components. Previously, componentshad to be substantially matched so that signal processing could produceacceptable results. By using the above invention, less thansubstantially matched components may be used together. Errors due to amismatch may be measured and compensated for by the predistortionsubsystem.

Referring to FIG. 8, a detailed block diagram of a system incorporatingthe features illustrated in FIG. 3, 4 and 7 is presented. As can beseen, the adaptive predistortion block 120 in FIG. 8 is comprised of theseparate magnitude delay 240 and phase delay 270 along with a magnitudepredistortion calculation block 260A. The inputs of these calculationblocks 230A, 260A are the delayed input signals from the delay blocks240, 270 and the adjusted feedback signals from the feedback signalprocessing block 400. After the magnitude and phase predistortionmodification are calculated, then the magnitude LUT block 220A and thephase LUT block 250A apply the predistortions. It should be noted thatthe magnitude LUT block 220A includes the magnitude LUT 220 and themagnitude LUT update block 230 shown in FIG. 3. Similarly, the phase LUTblock 250A incorporates the phase LUT 250 and the phase LUT update block260 illustrated in FIG. 3.

As can also be seen, the feedback signal processing block 400illustrated in FIG. 7 is comprised of the Cartesian to polar coordinateconversion block 340, the filtering module 337, and the demodulationmodule 335. Also included in the feedback signal processing block 400are the magnitude and phase adjustment blocks 410, 420.

A person understanding this invention may now conceive of alternativestructures and embodiments or variations of the above all of which areintended to fall within the scope of the invention as defined in theclaims that follow.

1-33. (canceled)
 34. A system for processing an input signal, the systemcomprising: an adaptive predistortion subsystem for receiving said inputsignal and for producing a predistorted signal by applying a deliberatepredistortion to said input signal; and a signal processing subsystemreceiving and processing said predistorted signal and producing a systemoutput signal, wherein said adaptive predistortion subsystem distortssaid Input signal to compensate for distortions in said system outputsignal; said signal processing subsystem decomposes said predistortedsignal into separate components, each of said separate components beingprocessed separately; said processing subsystem combines said componentsafter processing to produce said system output signal; and saiddeliberate predistortion applied to said input signal by said adaptivepredistortion subsystem to produce said predistorted signal is adjustedbased on said system output signal.
 35. A system according to claim 34wherein said signal processing subsystem comprises: a signal decomposerfor decomposing said predistorted signal into at least two components;at least two signal component processor blocks, each signal processorblock receiving an output of said signal decomposer and each signalprocessor block separately processes said output received from saidsignal decomposer; and a combiner receiving a processed output from eachof said at least two signal component processor blocks, said combinerproducing said system output signal from said processed outputs of saidat least two signal component processor blocks.
 36. A system accordingto claim 35 wherein at least one of said at least two signal componentprocessor blocks includes an amplifier.
 37. A system according to claim36 wherein said amplifier is a non-linear amplifier.
 38. A systemaccording to claim 34 wherein said system is part of a signaltransmission system.
 39. A system according to claim 34 wherein at leastsome of said distortions are due to said combiner.
 40. A systemaccording to claim 36 wherein said amplifier is a switch mode amplifier.41. A system according to claim 36 wherein said amplifier has a lowoutput impedance.
 42. A system according to claim 34 wherein saiddeliberate predistortion includes magnitude distortions which adjust amagnitude of said input signal.
 43. A system according to claim 34wherein said deliberate predistortion includes phase distortions whichadjust a phase of said input signal.
 44. A system according to claim 34wherein said deliberate predistortion is based on at least one entry ina lookup table.
 45. A method of processing an input signal to produce asystem output signal, the method comprising: a) receiving said inputsignal; b) applying a deliberate predistortion to said input signal toresult in a predistorted signal; c) decomposing said predistorted signalinto at least two component signals; d) combining said at least twocomponent signals to produce said system output signal; e) adjustingsaid deliberate predistortion based on said system output signal.
 46. Amethod according to claim 45 wherein said system output signal is an RFmodulated version of said input signal.
 47. A method according to claim45 further including a processing step of separately processing each ofsaid at least two component signals prior to step d).
 48. A methodaccording to claim 47 wherein said processing step includes amplifyingat least one of said at least two component signals.
 49. A methodaccording to claim 47 wherein said processing step includes phasemodulating at least one of said at least two component signals.
 50. Amethod according to claim 45 wherein step a) further includes the stepof accessing an entry in a lookup table, said deliberate predistortionbeing based on said entry.
 51. A method according to claim 50 whereinsaid deliberate predistortion is based on an interpolation of entries insaid table.
 52. A system according to claim 34 wherein saidpredistortion subsystem receives a replica of said system output signal.53. A system according to claim 35 wherein said deliberate predistortionis dependent on differences between said input signal and said replicaof said system output signal.
 54. A system according to claim 44 whereinentries in said lookup table are periodically updated based oncharacteristics of a replica of said system output signal.
 55. A systemaccording to claim 44 wherein said deliberate predistortion is based onan interpolation of entries in said table.
 56. A system according toclaim 34 wherein said predistortion subsystem includes: determiningmeans for determining said deliberate predistortion; adjustment meansfor applying said deliberate predistortion to said input signal; updatemeans for periodically updating said determining means based on saidsystem output signal.
 57. A system according to claim 56 wherein saidadjustment means receives parameters of said deliberate predistortionfrom said determining means.
 58. A method according to claim 45 furtherincluding the step of taking a difference between said input signal anda replica of said system output signal to determine said characteristicsof said system output signal.
 59. A method according to claim 50 furtherincluding the step of updating at least one entry in said table.
 60. Anadaptive predistortion subsystem for use with a signal processing systemwhich produces a system output signal, the predistortion subsystemcomprising: determining means for determining a deliberate predistortionto be applied to an input signal; adjustment means for applying saiddeliberate predistortion to said input signal; update means forperiodically updating said determining means based on characteristics ofsaid system output signal.
 61. An adaptive predistortion subsystemaccording to claim 60 wherein said adjustment means receives parametersof said deliberate predistortion from said determining means.
 62. Anadaptive predistortion subsystem according to claim 60 wherein saiddetermining means comprises a lookup table having entries, said entriesbeing used to determine said deliberate predistortion.
 63. An adaptivepredistortion subsystem according to claim 62 wherein said determiningmeans further comprises interpolating means for determining values notfound in said lookup table.
 64. An adaptive predistortion subsystemaccording to claim 60 wherein said deliberate predistortion is dependenton differences between said input signal and said replica of said systemoutput signal.
 65. A method according to claim 45 wherein saiddeliberate predistortion is at least partially based on characteristicsof said system output signal.
 66. A method according to claim 65 whereinsaid deliberate predistortion is determined in an iterative mannerduring transmission of said system output signal.
 67. A system accordingto claim 34 wherein said predistorted signal is adjusted based on saidsystem output signal and said input signal.
 68. A method according toclaim 45 wherein for step e), said deliberate predistortion is adjustedbased on said system output signal and said input signal.
 69. A systemaccording to claim 34 wherein said update means periodically updatessaid determining means based on said system output signal and said inputsignal.